有限温度下振转光谱的即时（on-the-fly）从头算半经典评估
On-the-fly ab initio semiclassical evaluation of vibronic spectra at finite temperature
AI总结：
本文将扩展 thawed Gaussian approximation 推广至非零温度，通过热场动力学转换演化方程，在不增加从头算电子结构计算成本的前提下，实现了对有限温度、非谐性及 Herzberg-Teller 效应的清晰区分，并成功应用于苯的对称禁戒吸收光谱评估。
摘要：
为了在零温下计算并分析振动分辨的电子光谱，我们最近实现了即时（on-the-fly）从头算扩展 thawed Gaussian approximation [A. Patoz et al., J. Phys. Chem. Lett. 9, 2367 (2018)]，该方法考虑了非谐性、模式-模式耦合和 Herzberg-Teller 效应。在此，我们将该方法推广以评估非零温度下的光谱。根据热场动力学，我们将密度矩阵相干分量的 von Neumann 演化转换为在自由度增加一倍的增广空间中波函数的 Schrödinger 演化。由于扩展 thawed Gaussian approximation 的高效性，坐标数量的增加几乎不产生额外的计算成本。具体而言，与原始的零温方法相比，有限温度方法不需要额外的从头算电子结构计算。同时，新方法能够清晰区分有限温度、非谐性和 Herzberg-Teller 效应对光谱的影响。我们在一个 Morse 模型系统上展示了有限温度 thawed Gaussian approximation 相对于常用全局谐振子方法的优势，并将其应用于评估苯的对称禁戒吸收光谱，其中上述所有效应均有贡献。
英文摘要：
To compute and analyze vibrationally resolved electronic spectra at zero temperature, we have recently implemented the on-the-fly ab initio extended thawed Gaussian approximation [A. Patoz et al., J. Phys. Chem. Lett. 9, 2367 (2018)], which accounts for anharmonicity, mode-mode coupling, and Herzberg-Teller effects. Here, we generalize this method in order to evaluate spectra at non-zero temperature. In line with thermo-field dynamics, we transform the von Neumann evolution of the coherence component of the density matrix to the Schrödinger evolution of a wavefunction in an augmented space with twice as many degrees of freedom. Due to the efficiency of the extended thawed Gaussian approximation, this increase in the number of coordinates results in nearly no additional computational cost. More specifically, compared to the original, zero-temperature approach, the finite-temperature method requires no additional ab initio electronic structure calculations. At the same time, the new approach allows for a clear distinction among finite-temperature, anharmonicity, and Herzberg-Teller effects on spectra. We show, on a model Morse system, the advantages of the finite-temperature thawed Gaussian approximation over the commonly used global harmonic methods and apply it to evaluate the symmetry-forbidden absorption spectrum of benzene, where all of the aforementioned effects contribute.
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